Shachiku (社畜): company livestock. The news site Limo defines it as a person who works sacrificing himself for the company he works for.
The origin of the word is uncertain. Limo says it is said to have been a buzzword of 1990. Mynavi News attributes it to the writer Azuchi Satoshi and dates its probable first use to a book of 1992.
Earlier labels for devoted workers were mōretsu shain, the fierce employee, and kigyō senshi, the corporate warrior.